Angiotensin II, a main vasoconstrictor hormone of renin-angiotension-aldosterone system (RAAS), plays an important role in pathological physiology of many chronic diseases. The production approach of Angiotensin II which is present in various tissues is mainly as follows: angiotensinogen acted on by renin can be converted to angiotensin I (Ang I) of decapeptide which only has little activity in contraction of blood vessel; and can be further converted by angiotensin converting enzyme to angiotensin II (Ang II) of octapeptide which is the final physiological active substance of renin-angiotension-aldosterone system (RAS) and can induce physiological functions such as contraction of blood vessel and elevation of blood pressure by binding to specific angiotensin II (ATII) receptor.
EP0253310 discloses a series of imidazole derivatives. Research of E. I. Du Pont de Nemours and Company (US) found that a compound of DUP753 has a good effect on lowering blood pressure. It was approved in 1994 and became the first non-peptide type Ang II receptor antagonist, i.e. losartan potassium, which inhibits contraction of blood vessel by selectively blocking the actions of angiotensin II of smooth muscle in blood vessel on its Ang I receptor to achieve the functions of dilating blood vessel and reducing blood pressure.
With the development and marketing of losartan potassium, various medical R&D organizations and companies began studies on structure of Ang II receptor antagonists in succession. U.S. Pat. No. 5,196,444 discloses a series of benzimidazole derivatives and processes for preparation thereof. Such derivatives have angiotensin II antagonistic activity and antihypertensive activity and thereby can be used to treat hypertensive diseases. Among them, candesartan was developed and marketed in 1997 by Takeda Chemical Industries, Ltd. (JP), which releases ester group in vivo and is hydrolyzed to its active metabolite to exert the action of lowering blood pressure.
U.S. Pat. No. 5,616,599 discloses a series of 1-biphenylmethylimidazole derivatives whose structures are similar to that of losartan. The significant difference in structure between them is that the chlorine atom at the 4-position of the imidazole ring of losartan is converted to 1-hydroxy-1-methylethyl and the 5-position of that is converted to a carboxyl group, hydroxyl group or pro-drug structures such as ester or amide. It is demonstrated to have good activity in reducing blood pressure. Therefore, Sankyo Company, Ltd. (JP) developed and marketed a drug of olmesartan.
Compared with other Ang II receptor antagonists marketed subsequently, losartan has more tolerance, fewer side effects and fewer possibilities to cause cough or edema. Studies have suggested that it is effective for reducing serum uric acid, TC and TG, and has no adverse effect on insulin sensitivity, insulin secretion and glucose tolerance of hyperinsulinism patients and is a safe antihypertensive drug. However, only 14 percent of losartan potassium can be metabolized in vivo to its active substance of EXP3174. Although losartan potassium itself has a strong activity in reducing blood pressure, its activity is only 3 percent of that of EXP3174. Molecular polarity of EXP3174 is too strong to get through the cell membrane by passive absorption forms such as diffusion. It is necessary to change its structure to improve its passive absorption.
U.S. Pat. No. 5,298,519 discloses a 5-position carboxyl esterified product of EXP3174, emphasizes on the research of a compound HN-65021, and discloses a test result of lowering blood pressure by oral administration of HN-65021 to show the compound has an activity of lowering blood pressure similar to that of losartan (British Journal of Clinical Pharmacology, 40, 1995, 591-593). It is indicated that converting 5-position carboxyl of the imidazole ring of EXP3174 molecule to a group with a smaller polarity is a tendency of the modification of losartan. It is required to convert the structure of EXP3174 molecule for getting an active compound with a better pharmacological effect of lowering blood pressure.
In summary, there is an urgent need to develop an active compound with an excellent effect of lowering blood pressure, a high efficiency of absorption and conversion and/or a high safety in this field.